Formation of boron-doped titanium metal films with high work function

ABSTRACT

A method for forming a Boron doped metallic film, such as Titanium Boron Nitride, is disclosed. The method allows for creation of the metallic film with a high work function and low resistivity, while limiting the increase in effective oxide thickness. The method comprises a thin metallic layer deposition step as well as a Boron-based gas pulse step. The Boron-based gas pulse deposits Boron and allows for the removal of excess halogens within the metallic film. The steps may be repeated in order to achieve a desired thickness of the metallic film.

FIELD OF INVENTION

The present disclosure generally relates to formation of a metallicfilm. In particular, the present disclosure relates to a method forforming a metallic film with a high electronic work function (“eWF”).

BACKGROUND OF THE DISCLOSURE

In applications such as the formation of pMOS metal gates, it isgenerally desirable to deposit a metal with a high work function and alow resistivity. A high work function allows for a lower thresholdvoltage offset and a lower off current. From this, a lower leakagecurrent can be achieved and a threshold voltage swing can be improved. Alow resistivity positively affects a cycle time and allows for higherspeed processing.

Formation of Titanium Nitride (“TiN”) films has been achieved usingdifferent methods. However, the TiN films created have exhibiteddifferent work functions based on the method used. For example, TiNfilms created through Atomic Layer Deposition (“ALD”) have demonstratedwork functions ranging between 4.70 and 4.75 eV. TiN films createdthrough plasma treatment with hydrogen gas in an EmerALD® XP ProcessModule from ASM International have demonstrated a work function ofapproximately 4.96 eV. TiN films created through Plasma Enhanced AtomicLayer Deposition (“PEALD”) treatment with Tantalum Carbon Nitride(“TaCN”) in an EmerALD® XP Process Module have demonstrated a workfunction of approximately 5.00 eV.

While the TiN films created through the plasma or PEALD treatment haveexhibited higher electronic work functions, plasma treatments have beendiscouraged for pMOS metal gate applications due to concerns over plasmadamage. In addition, the plasma treatments result in films with agreater Effective Oxide Thickness (“EOT”), which is known in the art asa thickness of a silicon oxide film required in order to produce thesame effect as a high-k material being used. A greater EOT isundesirable because it leads to a reduced capacitance.

Accordingly, a method that creates a metallic film with a highelectronic work function, low resistivity, and lower effective oxidethickness is desired.

SUMMARY OF THE DISCLOSURE

According to at least one embodiment of the invention, a method forforming a metallic film is disclosed. The method comprises a depositingstep of a thin metallic layer onto a semiconductor device and a pulsingstep of a gas onto the thin metallic layer. The depositing stepcomprises: (1) pulsing a metal halogen gas onto the semiconductordevice; (2) purging the semiconductor gas with an inert gas; (3) pulsinga nitridizing gas onto the semiconductor device; and (4) purging thesemiconductor gas with the inert gas. The pulsing step comprises: (1)pulsing a Boron-based gas onto the semiconductor device; and (2) purgingthe semiconductor device with an inert gas.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention havebeen described herein above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught or suggested herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments will becomereadily apparent to those skilled in the art from the following detaileddescription of certain embodiments having reference to the attachedfigures, the invention not being limited to any particular embodiment(s)disclosed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the inventiondisclosed herein are described below with reference to the drawings ofcertain embodiments, which are intended to illustrate and not to limitthe invention.

FIG. 1 illustrates a device in accordance with at least one embodimentof the invention.

FIG. 2 illustrates steps for a method in accordance with at least oneembodiment of the invention.

FIG. 3 illustrates steps for a method in accordance with at least oneembodiment of the invention.

FIG. 4 illustrates steps for a method in accordance with at least oneembodiment of the invention.

It will be appreciated that elements in the figures are illustrated forsimplicity and clarity and have not necessarily been drawn to scale. Forexample, the dimensions of some of the elements in the figures may beexaggerated relative to other elements to help improve understanding ofillustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it willbe understood by those in the art that the invention extends beyond thespecifically disclosed embodiments and/or uses of the invention andobvious modifications and equivalents thereof. Thus, it is intended thatthe scope of the invention disclosed should not be limited by theparticular disclosed embodiments described below.

Embodiments of the current invention relate to the doping of Boron intotitanium metal films, such as Titanium Nitride (“TiN”). The result is aBoron-doped metal film, such as Titanium Boron Nitride. The doping ofBoron into the formation of TiN films has shown promise as a result ofBoron's ability to remove excess chlorine in the film resulting from thepassing of Titanium Chloride (“TiCl₄”) gas. For example, Diborane ingaseous form reacts with the Chlorine in the film with the followingreaction.

B₂H₆ (g)+6Cl (in-film)→2BCl₃ (g)+3H₂ (g)

FIG. 1 illustrates a device made in accordance with at least oneembodiment of the invention. The device comprises: a substrate 10; asemiconductor channel 20; and a high-k semiconductor layer 30. Upon thisdevice, an undoped TiN underlayer 40 is deposited. This undoped TiNunderlayer 40 may be omitted. Above the undoped TiN underlayer 40 is aBoron-doped TiN layer 50. On top of the Boron-doped TiN layer 50 is anundoped TiN overlayer 60. As a result of this creation, the workfunction of the TiN device has ranged between 4.95 and 5.10 eV, whilelimiting an increase in an effective oxide thickness of the device.

FIG. 2 illustrates a method according to at least one embodiment of theinvention. The method may take place in a single chamber in-situ. Priorto this method, a device enters the single chamber. The device issimilar to the device illustrated in FIG. 1, prior to the addition ofthe Boron-doped layer and the overlayer.

The method comprises a depositing step 100, in which a thin metal filmis deposited. The method also comprises a pulsing step 200, in which thedeposited thin metal film is pulsed with a gas. The depositing step 100and the pulsing step 200 are explained in further detail below.

The method also comprises a first repeating step 300, in which thedepositing step 100 is repeated before heading to the pulsing step 200.The first repeating step 300 may occur as many times as necessary toform an appropriate thickness of the thin metal film. An appropriatethickness achieved through the first repeating step 300 may be less thanor equal to 10 Angstroms.

The method also comprises a second repeating step 400, in which thedepositing step 100 is repeated after the pulsing step 200 has beencompleted. The second repeating step 400 may occur as many times asnecessary to form an appropriate thickness of the metal film. Anappropriate thickness achieved through the second repeating step 400 mayrange between 20 and 100 Angstroms.

FIG. 3 illustrates the depositing step 100 in accordance with at leastone embodiment of the invention. The depositing step 100 first startswith a metal halogen pulse 110. The metal halogen pulse 110 has aduration ranging between 100 and 2000 milliseconds. Titanium Chloride(TiCl₄) is typically used as the gas in the metal halogen pulse 110.Other metal chlorides may be used in this step, such as ZirconiumChloride (ZrCl₄), Hafnium Chloride (HfCl₄), Vanadium Chloride (VCl₅),Niobium Chloride (NbCl₅), Tantalum Chloride (TaCl₅), Molybdenum Fluoride(MoF₆), or Tungsten Fluoride (WF₆). As a result of this step, a filmlayer of metal halogen is disposed on the device.

The Titanium Chloride pulse 110 is followed by an Inert Gas purge 120.The Inert Gas purge 120 has a duration typically exceeding 1000milliseconds. Typically, Argon (Ar) gas is used as the inert gas, thoughit may also be possible to use diatomic Nitrogen (N₂) gas in this step.The Inert Gas purge 120 removes excess precursor from the surface of thesemiconductor device and would also remove the excess precursor from thechamber. As a result of this step, excess reactant metal halogen gasfrom the metal halogen pulse 110 is removed from the device. Ideally,after the Inert Gas purge 120, a monolayer of the metal halogen gaswould be adsorbed to the device.

A Nitridizing gas pulse 130 follows the Inert Gas purge 120. TheNitridizing gas pulse 130 typically ranges in duration from 300 to 5000milliseconds. Typically, Ammonia (NH₃) gas is used for the Nitridizinggas pulse. It would be also possible to substitute Hydrazine (N₂H₂),Methyl Hydrazine, or Dimethyl Hydrazine for Ammonia. As a result of thisstep, a metal film is formed; for example, Titanium Nitride is formedfrom the reaction of Titanium Chloride with Ammonia.

The last step of the depositing step 100 is an Inert Gas purge 140. TheInert Gas purge 140 is much like the Inert Gas purge 120 and has aduration typically exceeding 1000 milliseconds. Also, Inert Gas purge140 will typically use Argon gas, though diatomic Nitrogen gas may alsobe used. The Inert Gas purge 140 removes excess precursor from thesurface of the semiconductor device and would also remove the excessprecursor from the chamber. As a result of this step, any excessreactant gas or byproducts would be swept away from the device.

FIG. 4 illustrates the pulsing step 200 in accordance with at least oneembodiment of the invention. The depositing step 200 first may startwith an optional metal halogen pulse 210. The optional metal halogenpulse 210 has a duration ranging between 100 and 2000 milliseconds. Thebenefit of this optional metal halogen pulse 210 is control over theamount of Boron doping. Similar to the metal halogen pulse 110, gasesused for the optional metal halogen pulse 210 can comprise: ZirconiumChloride (ZrCl₄), Hafnium Chloride (HfCl₄), Vanadium Chloride (VCl₅),Niobium Chloride (NbCl₅), Tantalum Chloride (TaCl₅), Molybdenum Fluoride(MoF₆), or Tungsten Fluoride (WF₆).

The optional metal halogen pulse 210 is followed by a Boron-based gaspulse 220. The Boron gas pulse 220 typically has a duration rangingbetween 100 and 2000 milliseconds. Typically, Diborane (B₂H₆) is usedfor the Boron gas pulse 220. As a result of this step, the Diboranereacts with the adsorbed metal halogen on the film to form gaseousproducts and a metallic film.

The last step of the pulsing step 200 is an Inert Gas purge 230. TheArgon purge 230 is similar to the Inert Gas purges 120 and 140, suchthat either Argon gas or diatomic Nitrogen gas may be used. The InertGas purge 230 has a duration typically exceeding 1000 milliseconds. TheInert Gas purge 230 removes excess precursor or byproducts from thesurface of the semiconductor device and would also remove the excessprecursor or byproducts from the chamber. As a result of this step, thegaseous products formed in the previous steps are removed.

The particular implementations shown and described are illustrative ofthe invention and its best mode and are not intended to otherwise limitthe scope of the aspects and implementations in any way. Indeed, for thesake of brevity, conventional manufacturing, connection, preparation,and other functional aspects of the system may not be described indetail. Furthermore, the connecting lines shown in the various figuresare intended to represent exemplary functional relationships and/orphysical couplings between the various elements. Many alternative oradditional functional relationship or physical connections may bepresent in the practical system, and/or may be absent in someembodiments.

It is to be understood that the configurations and/or approachesdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are possible. The specific routines ormethods described herein may represent one or more of any number ofprocessing strategies. Thus, the various acts illustrated may beperformed in the sequence illustrated, in other sequences, or omitted insome cases.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various processes,systems, and configurations, and other features, functions, acts, and/orproperties disclosed herein, as well as any and all equivalents thereof.

1. A method for forming a Boron-doped metallic film comprising:depositing a thin Boron-doped metallic layer onto a semiconductor devicein a chamber, the depositing step comprising: pulsing a metal halogengas onto the semiconductor device; purging the semiconductor device andthe chamber with an inert gas; pulsing a nitridizing gas onto thesemiconductor device; purging the semiconductor device and the chamberwith the inert gas; and pulsing a gas onto the thin metallic layer, thepulsing step comprising: pulsing a Boron-based gas onto thesemiconductor device to provide Boron in the Boron-doped metallic film;and purging the semiconductor device and the chamber with an inert gas.2. The method of claim 1, wherein the depositing step and the pulsingstep are repeated until a desired thickness of the Boron-doped metallicfilm is achieved.
 3. The method of claim 2, wherein the desiredthickness of the Boron-doped metallic film ranges between 20 and 100Angstroms.
 4. The method of claim 1, wherein the depositing step isrepeated until a desired thickness of the thin Boron-doped metalliclayer is achieved prior to the pulsing step.
 5. The method of claim 4,wherein the desired thickness of the thin Boron-doped metallic layer isless than or equal to 10 Angstroms.
 6. The method of claim 4, wherein anelectronic work function is modulated by a number of times thedepositing step is repeated.
 7. The method of claim 1, wherein the thinBoron-doped metallic layer comprises Titanium Nitride.
 8. The method ofclaim 1, wherein the pulsing step further comprises: pulsing a metalhalogen gas onto the semiconductor device prior to pulsing theBoron-based gas onto the semiconductor device.
 9. The method of claim 1,wherein the thin Boron-doped metallic layer formed exhibits anelectronic work function ranging between 4.95 and 5.10 eV.
 10. Themethod of claim 1, further comprising: depositing a thin underlayer ofundoped Titanium Nitride prior to the depositing step.
 11. The method ofclaim 1, further comprising: depositing a thin overlayer of undopedTitanium Nitride after the pulsing step.
 12. The method of claim 1,wherein the chamber is a single chamber in-situ.
 13. The method of claim1, wherein the steps of purging with an inert gas comprises purging withArgon gas for a duration exceeding 1000 milliseconds.
 14. The method ofclaim 1, wherein the step of pulsing with the metal halogen gas has aduration ranging between 100 and 2000 milliseconds.
 15. The method ofclaim 1, wherein the step of pulsing with the Nitrogen-based gas has aduration ranging between 300 and 5000 milliseconds.
 16. The method ofclaim 1, wherein the step of pulsing with the Boron-based gas has aduration ranging between 100 and 2000 milliseconds.
 17. The method ofclaim 1, wherein the metal halogen gas comprises at least one of:Titanium Chloride, Zirconium Chloride, Hafnium Chloride, VanadiumChloride, Niobium Chloride, Tantalum Chloride, Molybdenum Fluoride, orTungsten Fluoride.
 18. The method of claim 1, wherein the Boron-basedgas comprises Diborane.
 19. The method of claim 1, wherein thenitridizing gas comprises at least one of: Ammonia, Hydrazine, MethylHydrazine, or Dimethyl Hydrazine.
 20. The method of claim 1, wherein theinert gas comprises at least one of: Argon or diatomic Nitrogen.